This application relates to the art of making polybenzazole fibers.
It is well known to polymerize polybenzazole polymers in polyphosphoric acid solutions, so that an acid dope is formed. The resulting dopes are spun and drawn to make fibers. The dope fibers are coagulated by contact with a liquid that dilutes the solvent, and the residual acid is washed from the fibers. See, e.g., Wolfe et al., U.S. Pat. No. 4,533,693 (Aug. 5, 1985) which is incorporated herein by reference.
The coagulation and leaching steps can become a significant bottleneck in a continuous production process, because they are very time-consuming. Commercially desirable fibers should contain no more than about 2000-5000 ppm phosphorus, and lower levels may be useful for some purposes. (Residual solvent acid is usually expressed in terms of parts-per-million (ppm) of residual phosphorus in the fiber, because common tests measure the quantity of phosphorus in the fiber. The quantity of residual acid can easily be calculated from the residual phosphorus.)
On the other hand, long leaching times are unacceptable in commercial production, because the fiber is spun at a very rapid rate and needs to be washed at an equally rapid rate.
What is needed is an accelerated process to coagulate and leach polybenzazole fiber.